Tall oil is a by-product of alkaline pulping processes of resinous wood species for the manufacture of chemical pulps. It is well known to be a combustible substance. Typically, its calorific value ranges from 35 to 40 MJ/kg. Indeed, the burning the tall oil in power boilers is a common practice in many industrial plants. Over the years, various attempts have been made to use tall oil as a fuel for internal combustion engines. Because of its high viscosity at ambient temperatures, tall oil has frequently been diluted with mineral oil, such as diesel oil. Moncrieff British Patent No. 821,825 discloses the use of tall oil as a stabilization agent in a fuel for an internal combustion engine comprising a blend of mineral oil and alcohol. White U.S. Pat. No. 2,686,713 and Eckert Canadian Pat. No. 914,411 disclose the use of tall oil derivatives as additives to inhibit the corrosivity of commercial diesel fuel, kerosine and gasoline.
It is known by those skilled in the art that a fuel blend comprising crude tall oil and mineral oil or vegetable oil causes frequent plugging of the fuel filter of internal combustion engines. In the past this has seriously discouraged the use of tall oil as a fuel for internal combustion engines. The plugging of the fuel filter has been found to be mainly caused by the ubiquitous presence of lignin-like dispersed substances in the crude tall oil. These lignin-like substances are well dispersed and not easy to remove by conventional means.
In Sullivan U.S. Pat. No. 2,838,481 issued June 10, 1958, a process is described in which a mixture of tall oil and water is heated to about 82.degree. to 93.degree. C., whereby 95 to 98 percent of lignins present are removed. Palmqvist U.S. Pat. No. 3,948,874 issued Apr. 6, 1976 describes and illustrates a method for removing lignin from tall oil in which tall oil obtained after removal of splitting liquid (water) is dried by heating to, for example, 90 to 95 degrees C. This drying process increases the acidity of the tall oil and thereby precipitates lignin. Neither of these prior art references, however, discloses a suitable method of adapting tall oil for use as a fuel for internal combustion engines or a product which would be useful in this way.
Another reference of general background interest, describing the processing of tall oil is U.S. Pat. No. 2,908,676 of Van Valkenburgh issued Oct. 13, 1959.
It is an object of the present invention to provide a fuel blend incorporating tall oil which will be effective for use in internal combustion engines, and which will have reduced contents of lignin-like substances thereby providing extended life to fuel filters of internal combustion engines.